Re-start animation if message is sent again?
Disable the continue option on the action actuator and put the script between the sensor and the action actuator :


when the sensor send a pulse the script will be triggered 
if there is action being played on layer 0 the script will stop stop it
the script passes the pulse to the actuator




cont = bge.logic.getCurrentController()
own = cont.owner

if own.isPlayingAction(0):
    own.stopAction(0)
cont.activate("Action")